I am using a TabView/NavigationView & NavigationLink to programmatically navigate from a list view to detailed view and when I update the boolean property 'pinned' to true & save the core data entity in the detailed view, I am getting the following unfortunate side effects:
- an involuntary navigation back to the list view and then again back to the detailed view or
- an involuntary navigation to another copy of the same detailed view and then back to the list view.
I have prepared a small Xcode project with the complete sample code
In the list view I use @FetchRequest to query the list and sort on the following:
@FetchRequest(entity: Task.entity(),sortDescriptors: [NSSortDescriptor(key: "pinned", ascending: false),
NSSortDescriptor(key: "created", ascending: true),
NSSortDescriptor(key: "name", ascending: true)])
In the list view I use the following:
List() {
ForEach(tasks, id: \.self) { task in
NavigationLink(destination: DetailsView(task: task), tag: task.id!.uuidString, selection: self.$selectionId) {
HStack() {
...
}
}
}
.
(1) If I omit the 'NSSortDescriptor(key: "pinned" ...)' I don't see the behavior.
(2) If I omit the 'tag:' and the 'selection:' parameters in the NavigationLink() I don't see the behavior. But I need to be able to trigger the navigation link programmatically when I create a new Task entity.
(3) It seems never to happen when I have a single entity in the list or changing the value of the 'pinned' boolean property in the first entity in the list.
(4) I get the warning:
[TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window)...
The parent view to the list view (TasksListView) contains a TabView:
struct ContentView: View {
var body: some View {
TabView {
NavigationView {
TasksListView()
}
.tabItem {
Image(systemName: "tray.full")
.font(.title)
Text("Master")
}
NavigationView {
EmptyView()
}
.tabItem {
Image(systemName: "magnifyingglass")
.font(.title)
Text("Search")
}
}
}
}
struct TasksListView: View {
// NSManagedObjectContext
@Environment(\.managedObjectContext) var viewContext
// Results of fetch request for tasks:
@FetchRequest(entity: Task.entity(),sortDescriptors: [NSSortDescriptor(key: "pinned", ascending: false),
NSSortDescriptor(key: "created", ascending: true),
NSSortDescriptor(key: "name", ascending: true)])
var tasks: FetchedResults<Task>
// when we create a new task and navigate to it programitically
@State var selectionId : String?
@State var newTask : Task?
var body: some View {
List() {
ForEach(tasks, id: \.self) { task in
NavigationLink(destination: DetailsView(task: task), tag: task.id!.uuidString, selection: self.$selectionId) {
HStack() {
VStack(alignment: .leading) {
Text("\(task.name ?? "unknown")")
.font(Font.headline.weight(.light))
.padding(.bottom,5)
Text("Created:\t\(task.created ?? Date(), formatter: Self.dateFormatter)")
.font(Font.subheadline.weight(.light))
.padding(.bottom,5)
if task.due != nil {
Text("Due:\t\t\(task.due!, formatter: Self.dateFormatter)")
.font(Font.subheadline.weight(.light))
.padding(.bottom,5)
}
}
}
}
}
}
.navigationBarTitle(Text("Tasks"),displayMode: .inline)
.navigationBarItems(trailing: rightButton)
}
var rightButton: some View {
Image(systemName: "plus.circle")
.foregroundColor(Color(UIColor.systemBlue))
.font(.title)
.contentShape(Rectangle())
.onTapGesture {
// create a new task and navigate to it's detailed view to add values
Task.create(in: self.viewContext) { (task, success, error) in
if success {
self.newTask = task
self.selectionId = task!.id!.uuidString
}
}
}
}
}
struct DetailsView: View {
// NSManagedObjectContext
@Environment(\.managedObjectContext) var viewContext
@ObservedObject var task : Task
@State var name : String = ""
@State var dueDate : Date = Date()
@State var hasDueDate : Bool = false
@State var isPinned : Bool = false
var body: some View {
List() {
Section() {
Toggle(isOn: self.$isPinned) {
Text("Pinned")
}
}
Section() {
TextField("Name", text: self.$name)
.font(Font.headline.weight(.light))
Text("\(task.id?.uuidString ?? "unknown")")
.font(Font.headline.weight(.light))
}
Section() {
HStack() {
Text("Created")
Spacer()
Text("\(task.created ?? Date(), formatter: Self.dateFormatter)")
.font(Font.subheadline.weight(.light))
}
Toggle(isOn: self.$hasDueDate) {
Text("Set Due Date")
}
if self.hasDueDate {
DatePicker("Due Date", selection: self.$dueDate, in: Date()... , displayedComponents: [.hourAndMinute, .date])
}
}
}
.navigationBarTitle(Text("Task Details"),displayMode: .inline)
.navigationBarItems(trailing: rightButton)
.listStyle(GroupedListStyle())
.onAppear() {
if self.task.pinned {
self.isPinned = true
}
if self.task.name != nil {
self.name = self.task.name!
}
if self.task.due != nil {
self.dueDate = self.task.due!
self.hasDueDate = true
}
}
}
// save button
var rightButton: some View {
Button("Save") {
// save values in task & save:
self.task.pinned = self.isPinned
if self.hasDueDate {
self.task.due = self.dueDate
}
if self.name.count > 0 {
self.task.name = self.name
}
Task.save(in: self.viewContext) { (success, error) in
DispatchQueue.main.async {
if success {
print("Task saved")
}
else {
print("****** Error: Task can't be saved, error = \(error!.localizedDescription)")
}
}
}
}
.contentShape(Rectangle())
}
}
extension Task {
static func save(in managedObjectContext: NSManagedObjectContext, completion: @escaping (Bool, NSError?) -> Void ) {
managedObjectContext.performAndWait() {
do {
try managedObjectContext.save()
completion(true, nil)
} catch {
let nserror = error as NSError
print("****** Error: Unresolved error \(nserror), \(nserror.userInfo)")
completion(false, nserror)
}
}
}
}
Any suggestions?
